Tape laying machines are well known in the art for making various composite plastic structures including components for aircraft, components for automobiles and part for ships. These machines have a tape laying head, usually oriented around a tape laying path, that includes a presser member for applying force against the tape to detrude the tape onto the work surface while following the changing contour of the work surface (e.g. mold). Such a tape machine is described in U.S. Pat Nos. 4,557,783 and 4,954,204, assigned to the assignee of this application, the entire disclosures of which are incorporated herein by reference. U.S. Pat. No. 4,954,204 more specifically describes a presser member employing a segmented shoe.
The tape is customarily a thermosetting or thermoplastic film often having fibrous (e.g. glass or carbon fibers) reinforcement embedded therein. Such tape is applied to the work surface by a presser member with some amount of pressure or force, in layers that are subsequently further consolidated, often with heat and pressure.
More recent designs of tape laying machines, for making composite plastic structures, employ a segmented shoe in the presser member. The segmented shoe customarily has a plurality of individually movable parallel plates or individually movable rollers which provide the advantage of improved conformation of the tape to the work surface, especially when simultaneous multiaxial changes in contour occur on the work surface. To further improved the performance of the segmented shoe it is known to use a flexible skid member (e.g. a sheet of tough flexible material) between the shoe (i.e. the shoe segments) and the tape. This flexible skid can allow easier movement of the shoe over the tape.
In the laying of the plastic tape onto the work surface or a previously laid layer of tape the tape laying machines start with the head and more particularly the presser member at some initial location near but off of the desired contact point with the work surface or previously laid layer of tape. However the exact position of the contact point with the work surface, especially the exact vertical axis position of the work surface with respect to the tape laying head, is not known with sufficient accuracy and/or may vary such that stopping the downward movement of the head at the proper time the presser member engages the work surface is often very difficult to achieve. From the initial location the head and more particularly the segmented shoe presser member, with all the segments of the shoe brought to the same position in the shoe known as the null position, is brought to the edge or other predetermined position of the work surface or previously laid layer of tape by the machine controls manually or under the direction of a computer program. As the segmented shoe engages the work surface, in an approach that has the longitudinal axis of the segmented shoe at some angle to the edge of the work surface, the head and its presser member move vertically and laterally with respect to the work surface and pressure is applied to the shoe segments for compacting the tape onto the work surface. When one or more segments of the shoe engage the edge of the work surface they are raised leaving the other non-engaging segments down with respect to both the engaging segments and the work surface. This condition causes the tape, which is lying across the width of the segmented shoe, to become distorted (i.e. twisted) with the downward movement of the head before such movement of the head is stopped. To overcome this problem the prior art has employed manual adjustment of the downward movement of the head, including the presser member and/or a shim to provide a resting surface for the segments of the shoe that do not initially engage the work surface, so that all of the segments are positioned at the same vertical location as those initially engaging the work surface as the shoe proceeds on to the work surface laying tape.
Since the shim is located at the edge of the work surface where the shoe is to engage the work surface the position of the shim and the work surface edge may be included in a computer program to control the movement of the tape laying machine head for engaging the work surface and laying tape. However this system requires a shim to be positioned at each place where the presser member of the head engages the work surface to lay down a course of tape thus adding to the complexity of the tape laying machine and process. Additionally it is not always appropriate, desirable or possible to employ a shim or manual control of the head movement for engaging the work surface, particularly with a segmented shoe presser member. Thus a more effective, accurate, efficient and automated apparatus and method for bringing a segmented shoe into engagement with a work surface, from a non-engaging location, for laying plastic tape thereon is both needed and desirable.